1. Field of the Invention
The invention relates to a process for rectifying product phenol obtained by the acid-catalyzed decomposition of cumene hydroperoxide.
2. Description of Related Art
Phenol produced by the acid-catalyzed decomposition of cumene hydroperoxide is conventionally purified via a series of distillations in which progressively heavier components of the decomposition mixture are separated as overheads.
The decomposition product is neutralized, typically in an alkaline ion exchanger, before being separated into products phenol and acetone, by-products, and unreacted cumene for recycle.
The decomposition mass is separated sequentially into acetone, cumene, alpha-methylstyrene (AMS), phenol and high boiling residues. Phenol, acetone and AMS are further purified into end products. Recovered cumene is caustic washed to rid it of acidity before recycle to oxidation. The separation of the crude decomposition mass is carried out in a series of fractionating distillation columns in commercial operation.
Phenol purification is carried out in vacuum distillation columns usually equipped with from 30 to 40 vapor-liquid counter current contact trays or equivalent height of mass transfer packed beds.
Considerable amounts of phenol remain with higher boilers in the bottoms of the final distillation column in which product phenol is rectified, and obtained as an overhead stream.
To insure adequate quality for the phenol in the overheads, typically greater than 15% phenol is left in the bottoms of such phenol rectification column, along with heavy impurities such as acetophenone, cumylphenol, alpha-methylstyrene dimers (AMS dimers) and other high boilers (residue). Although an attempt is made in a subsequent residue column to recover more phenol, albeit of a lesser quality, in order to reduce the amount lost with high boilers in those bottoms, phenol still represents at least 5% of the total residual high boilers. These are usually burned to recover only heat values.
Furthermore, the overheads of such subsequent residue column, predominantly phenol, contain too much acetophenone to be acceptable as product, thus are recycled upstream in the process, for rework.
U.S. Pat. No. 4,415,409 to Zudkevitch et al. discloses a process for extractive distillation of phenol and acetophenone using cumylphenol as an extractive solvent. However, this patent does not teach or suggest the combination of distillation steps and the added advantages of the process claimed herein.